Wind turbines which operate with variable rotational speed may comprise an indirect grid connection where AC current from the generator with variably frequency can be converted to AC current with a fixed frequency of the utility grid.
The conversion is usually done by a rectifier conversion into direct current (AC/DC) followed by a controlled inverter conversion into a fixed frequency (DC/AC). Accordingly the generator of the wind turbine is connected to a rectifier which is connected to an inverter producing the AC current which is needed for a power grid. Commonly the conversion of DC into AC in the inverter can be done by using either thyristors or transistors. One advantage of this indirect grid connection is that it is possible to run the wind turbine at variable speed allowing the rotor to vary in speed thereby adapting to the aerodynamic conditions.
In EP 1 768 223 A2 a wind turbine is disclosed using converter modules. The converter module comprises a generator contactor for disconnecting the generator from the electronics of the converter modules. The converter module also comprises an inductor for smoothing the generator current, a generator inverter for transforming the AC signal from the generator to a DC signal, a DC link capacitor for smoothing out variations for the DC signal, a break chopper for dissipation of residual power, a grid inverter for transforming the DC signal into an AC signal, and an inductor which in combination with capacitors serves to reduce harmonics of the voltage signal being applied to the utility grid. The converter module further comprises a charge resistor for charging the DC link capacitor when the charge contactor is closed, a grid contactor for disconnecting the utility grid from the electronics of the converter module and a circuit breaker for disconnecting the utility grid from the converter module in case of an overcurrent.
In WO 2010/083903 A2 a wind turbine comprising a generator contactor for disconnecting the generator from the electronics of the converter module is disclosed. The generator contactor is mounted in receiving spaces of the rotating magnet wheel housing.